The diffraction focusing phenomenon of water waves has been considered for enhancing wave-energy. In particular, the diffraction focusing phenomenon of water waves for energy conversion was initially proposed by Budal and Falnes in their paper “A Resonant Point Absorber of Ocean Waves”, Natures, Vol 256, pp. 478-479 (1975). Those authors called small bodies producing the phenomenon “point-absorbers”. Essentially, it is a focusing of incident wave energy on a small body resonating in one or more modes with the incident wave. In short, the body acts as a hydrodynamic antenna. “Ocean Wave Energy Conversion” by M. E. McCormick, published by Wiley-Interscience, New York (1981, reprinted by Dover Publication, Long Island, N.Y. in 2007) refers to the phenomenon as “antenna focusing”. The focusing effect is due to a destructive interference between the waves radiated from the body on the incident waves. Budal and Falnes produced a number of papers illustrating how point-absorption could enhance wave-energy conversion. The book entitled “Ocean Wave Oscillating Systems” by Falnes, published by Cambridge University Press, 2002 includes a summary of the findings of these two investigators. In wave-energy conversion by a point-absorber, the conversion must be “active” in the sense that a turbine or some other type of power take-off system must be used. In addition, a control system should be incorporated. Recent advances in both power take-off and control subsystems are presented in the proceedings of the European Wave and Tidal Energy Conference, held in Sweden in September, 2009. See “Comparison of Wave Power Extraction by Compact Array of Small Buoys and by a Large Buoy”, Proceedings, 8th European Wave and Tidal Energy Conference, Uppsala, Sweden, Sep. 7-10, Paper VII-C-1.
The diffraction focusing phenomenon of water-wave energy caused by floating body motions (heaving, surging or pitching) have been shown to provide the ability of relatively small bodies to capture wave energy from crest widths that are several times the body's horizontal dimension. As is known, such moving bodies act as “antennae” to produce radial waves which destructively interact with the incident waves, causing a transfer of energy (by diffraction) along the crest to the body. Thus, such bodies have been proposed for forming floating breakwaters. Floating breakwaters of various types have been in existence for many decades since, they are deployed with relative ease, and have less environmental consequences compared to rock structures. The effectiveness of floating breakwaters, however, is somewhat less than near-shore armor breakwaters. Normally, floating breakwaters, designed to protect the leeward waters, have extensive lengths that are parallel to the crest width of the design wave. The units can be either continuous in the crest direction or segmented.
Arrays of buoys have also been studied for the purpose of shore protection, where the spacing between the component buoys is relatively small. In all of these cases, the units are designed to resonate with a wave having a specific period, T, with no regard to the actual impedance of the system.
A recent study of the effects of buoy impedance is that of Liang, Huang and Li in their article “A Study of Spar Buoy Floating Breakwater”, in Ocean Engineering, Vol. 31, No. 1, pp. 43-60 (2004). In that study, tension-moored spar buoys of deep draft equipped with damping plates are proposed for shore protection. The buoys absorb energy by heaving motions, and dissipate the energy in the alternating wakes of the damping plates. The focus of the study is on the effectiveness of the damping plates on the closely packed arrays of spar buoys. Other floating breakwater configurations include cages, as discussed by Murali and Mani in their article “Performance of Cage Floating Breakwater”, Jl. Of Waterway, Port, Costal and Ocean Engineering (ASCE), Vol. 123, No. 4, pp. 172-179 (1997), tube-nets and spheres, as discussed by Twu and Lee in their article “Wave Transmission in Shallow Water through the Arrangements of Net Tubes and Buoyant Balls”, Proceedings, 7th Conf. on Ocean Engineering, Taipei, Vol. II, pp. 26, 1-26, 21 in Chinese (1983). All of these rely on a “brute force” method of extracting and dissipating the wave energy. That is, there is little sophistication in the design as far as the impedance is concerned. Furthermore, by design, the breakwaters are impassible since they are either long and continuous or in closely packed arrays.
Thus, there presently exists a need for a floating breakwater which overcomes the disadvantages of the prior art. The subject invention addresses that need.